Broad-banded termination for electromagnetic wave transmission systems



April 1, 1952 N. R. WILD BROAD BANDED TERMINATION FOR ELECTROMAGNETIC WAVE TRANSMISSION SYSTEMS Filed July 26, 1945 I/flfi/HBLE FREQUENCY u;

050/; 1. firm /A/l A/ 7'04 Patented Apr. 1, 1952 BROAD-BANDED TERMINATION FOR ELEC- TROMAGNETIC WAVE TRANSMISSION SYSTEMS Norman R. Wild, East Natick, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application July 26, 1945, Serial No. 607,125 1 Claim. (01. 17844) it has special application as a phantom plunger for maintaining constant, over a frequency band of appreciable width, the terminal impedance of a variable-frequency generator.

Terminal devices of the general character indicated most generally comprise a wave guide section provided at one end with a shorting plunger, said plunger being movable within said wave guide section to alter the efiective electrical length thereof and thereby cause the same to resonate at different frequencies. In order to extract maximum power from the system with which'such aterminal device is associated, it is, of course; necessary to retune the terminal device whenever any change is made in the frequency of the energy being conveyed by the system.

Consider the case of a variable-frequency generator whose output is developed, for example, in a toroidal cavity resonator which, in turn, is coupled to a wave guiding system. In order to insure proper phase relationship, at the point of coupling of the toroid to the wave guiding system,

between the energy developed in various regions of the toroid, it is usually necessary to provide, at a point diametrically opposite to the point of said coupling, a wave guide section having a plunger therein to tune the same; and whenever the generator frequency is changed, said wave guide section must be retuned.

The disadvantages of such a system are obvious, and it is to the elimination of these disadvantages that my present invention is primarily addressed.

It is, therefore, the main object of my present invention to provide a terminal device for an energy-transmission system, especially, at the oscillator end of such a system, whereby the terminal impedance and, hence, the frequency response, remain substantially constant over, at least, an appreciable portion of the frequency band of the energy being conveyed.

It is a further object of my present invention to provide a terminal device which will accomplish the foregoing automatically, that is, without requiring any manual tuning.

These, and other objects of my present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly, in the following manner:

The terminal device of my present invention comprises, in a general sense, a broad-banded or low-Q cavity resonator, the Width of the frequency band over which the response of said cavity resonator is substantially constant being determined by the size, and the location with respect to said cavity resonator, of an iris, by means of which said cavity resonator is coupled-to the energy-transmission system.

I have found that by the use of such a broadbanded cavity resonator, the terminal impedance of the system remains substantially constant, and maximum power is, therefore, obtained at all of the frequencies within the band.

In the accompanying specification I shall describe, and in the annexed drawing show, an illustrative embodiment of the energy-transmission system of my present'invention. It is, however, to be clearly understood that I do not Wish to be limited to the details herein shown and described for purposes of illustration only, inasmuch'as changes therein may be made without the exercise of invention, and within the true spirit and scopeof the claims hereto appended.

In said drawing, thesingle figure is a partial side elevational, partial longitudinal sectional view of an energy-transmission system provided with a terminal device made in accordance with the principles of my present invention.

Referring now more in detail to the aforesaid illustrative embodiment of my present invention, and with particular referenceto the drawing illustrating the same, the numeral 5 designatesa variable-frequency oscillator adapted to generate electromagnetic energy in the microwave region of the frequency spectrum. As indicated in earlier portions of thi specification, such an oscillator may include a cavity resonator (not shown) coupled, by conventional methods, to a wave guiding system, for example, to a hollow, cylindrical pipe 6. As also indicated in earlier portions of this specification, such a cavity resonator is usually provided, at a point opposite its coupling to the wave guiding system, with a wave guide section. 1 which, heretofore, has generally included a tuning plunger for resonating the same to the various frequencies generated by the oscillator 5.

By means of my present invention, said tuning plunger is eliminated, and, instead, I couple to the wave guide section 1, as at 8, another wave guide section 9 having, at its outer end, a conventional choke coupler ID by means of which communication is established between said Wave guide section 9 and the terminal device H of my present invention.

erably, in the vicinity of the frequency of the oscillator The entrance to the recess I3 is closed by a plate M which may be made, for example, of copper, and which is provided with an iris l5 for coupling the cavity resonator to the open end of the choke coupler II].

In a. particular case, I provided th cylindrical body l2 with a recess [3 having a diameter of .514" and a depth of .530. I found this structure to have a resonant. frequency corresponding to a wave length of 1.600 cm. I then closed the recess l3 with a plate l4 having a central iris of .098" in diameter. I found that the resulting cavity resonator had a substantially uniform frequency response over a band extending' from approximately 1.458 cm. to approximately 1.492 cm. I further found that by locating the iris somewhat olf center, the band width, over which uniform response could beobtained,

dropped to approximately 1.470 cm. to approximately 1.490 cm.

Now, the cavity resonator alone is equivalent to a high-Q, parallel-tuned circuit, and the Q thereof may be lowered, so as to broad-band the same whereby its frequency response will be made constant over the desired frequency band, in the case under consideration, an appreciable portion, at least, of the band of the oscillator 5, by properly dimensioning the iris l5, and by properly locating said iris with respect to the axis of the recess l3.

While the iris hasv here been shown to be centrally located in the plate I4, it will be understood that it can be off center, its central location resulting, however, in the maximum uniform frequency response.

The cavity resonator l2 and the plate l4 may be secured to the choke coupler III by means of bolts [6.

I have found that terminal devices, such as has been described, causes the energy-transmission system with which it is associated to have a substantially constant terminal impedance over an appreciable frequency band, as a result of which, maximum power can be extracted from the oscillator 5 at all of the frequencies at which said oscillator is adapted to operate.

This completes the description of the terminal devices of my present invention. Other objects and advantages thereof, in addition to those specifically set forth herein, will'be obvious to those skilled in the art to which the same relates.

What is claimed is:

In combination: a variable-frequency generator of electromagnetic energy in the microwave region of the spectrum; means coupled to said generator for conveying the generated energy, in one direction to a load, and in another direction 7 to a terminal device; said terminaldevice having a constant impedance over the frequency. band of said generator and comprising a low-Q cavity resonator provided with a coupling iris.

NORMAN R.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Number Name Date 2,106,771 Southworth Feb. 1, 1938 2,155,508- Schelkunofi Apr. 25, 1939 2,200,023 Dallenbach May 7, 1940 2,375,223 Hansen May 8, 1945 2,405,217 Labin Aug. 6, 1946 2,453,453 Norton Nov. 9, 1948 2,473,448 Rieke June 14, 1949 

